Prototype Windmill Power curve

[joseba1]

Hey all,

 I just created a power curve for my prototype volumetric, variable oriented axis wind turbine.  I know, a mouthfull!  I developed this curve using a prony brake and a lot of data, 1000s of readings. it looks pretty good.  The unit is 74" diameter and for comparison I used a Skystream 3.7(12')  power curve developed by a french organization called SEPEN.  (To find that information search for "gipe skystream sepen"). Because their unit is about 12' and mine is about 6' I quartered their data.

The question I have is this a valid way to look at this?  I'm looking for people to shoot a few holes in my results so  take aim!!!

If you want to learn more about my testing I have copius documentation, that I will gladly include if requested.

I'll check  back periodically to see if I have anything left.



Thanks

[SparWeb]

Many questions come to mind...  getting them in order is the hard part.

What are you measuring?  I mean what machine are you looking at?  What are you talking about?  Do you have a photograph?  Any description?

The skystream data is electrical production under statistically averaged conditions and in service in a particular test location, with all the losses that includes.  Your test compares to that how??

[joseba1]

Patent pending...I don't want to disclose too much.  My aim here is to figure out if I'm missing anything.

The rotor's Diameter is 74"
The Speed measuring device is a Specialize cycling computer.
The wind speed meter is just a hand held anemometer located just below midway in front of the rotor
The  scales or two digital rapala 50lb fish scales...( I do not recommend these for testing, they kept turning off)

I've attached a redacted photo of one of the test pictures.  To record RPM, I used the cyclometer,(the red object), to arrive at rpm multiply the speed reading by 9.  The wind speed meter is the black object next to the two Rapala fish scales. The pulley is 6" diameter made of plywood.  The Belt is made of 3 layers of nylon webbing with copius amounts of a substance called "Belt Grip".  My first attempt was a wrap of polypropylene rope which burned through in about 20 minutes.  I felt like Roy Schneider in Jaws, '...think I'm going to need a bigger brake.'  I had a rope tied to a lever tied to the "high side" fish scale the low side fish scale was tied to a member on the support.  My camera and myself were located about 30 feet upwind.

Why it's volumetric, All the typical hawts measure their power based on planar geometry even though in reality they are not acutually planar.  They compress their 3dness into a very short space resulting in a twist in the blade, (which by the way makes it more difficult to manufacture).  This blade does not sport a twist. I expanded the geometry outward.

Also the typical blades are high aspect ratio type blades, sort of like an albatross, this rotor's blade is more like an eagle or an owl capable of pulling heavy objects from the water.  Very low aspect ratio. 

The Spreadsheet is from an afternoon of testing

[taylorp035]

Not to be too skeptical, but I have a hard time believing that there is that much power in the wind at low speeds.  The cubic nature of the equation that dictates how much power you can extract out of the wind would probably not make a graph like that if the wind speeds were calibrated correctly.

[joseba1]

I know, the results seem incredible!

As far as calibration is concerned...I've checked and double checked. 
The scales are correct, I checked them with known weights and switched them around to see if they were off. 
The cyclometer is correct but I would've been happier with something with a hall effect sensor.  The delay causes an increase in variability that I have to take an incredible amount of readings to compensate for. 

Which brings me to the wind meter I checked it by holding it outside of the car going the readings were pretty close to the speed of the car. It could be the wind speed at the level where the meter was, slightly below center on the rotor, gave a too low reading but the rotor was being effected by the same, speed of wind at that level so overall it should be only slightly lower.

This attached is a version of the input spreadsheet

[joseba1]

I think the Skystream data is definatly subject to losses and so is mine, I suspect their electrical generation capabilities are somewhere close to 90% of mechanical.  If not, why not?

At low wind speed they aren't generating anything, and that I believe that to be typical.

If you are familiar with sailing, on days with very little wind you put up the biggest sail you have.  I've got a very big sail. and I'm deliberatly trying to generate more at low wind speeds.  It seems to be working.

[GoVertical]

power lost at the stator adds a lot confusion, solution add a MPPT controller to the system

[oneirondreamer]

I also have used a variety of Proney brakes to measure shaft power of my turbine.    As your power curve does seem very good, things I would check are accuracy of wind speed in, your instrument could be interacting with your turbine,   I'd see if you could move it laterally.    I'd think it should be at least a few rotor diameters away.   

The other thing with they type of Proney brake you are using, if I am correct, it's load a - load b to get force.    It's easy to assume that it's load a + load b = force.   If your RPM's are low and the friction uneven, resonance between the springs in the scales can cause havoc too.

[oneirondreamer]

I just looked over your spreadsheets.    None of the formula's seem present, so it's hard to check that.   In looking at your data what I'm seeing is a TSR that goes from 11.8 at 1.9 (m/s?) to  3 or 4 at 8 m/s.   That seems odd to me, both in that 11 would be a very high TSR for a turbine, and to have the same turbine produce optimal power at such very different TSR's seems odd.    I have gone through huge headaches getting instrumentation right, I can imagine you may have the same issue.   I'm now using vernier equipment, a logger pro logger, with a optical position reader for turbine speed, a load cell for force from Proney brake (or V and A sensors for watts out), and a wind speed indicator.    It's saved me huge headaches.